Pulse Generator (Thyristor)

Generate pulses for twelve-pulse and six-pulse thyristor
converters

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Control and Measurements/Pulse & Signal Generators

Description

The Pulse Generator (Thyristor) block generates two pulse trains.
These control a twelve-pulse thyristor converter made of two three-phase
full-wave thyristor bridges (also called Graetz bridges). In steady-state
condition, each pulse train consists of six equidistant square pulses
with 60 degrees shift between them.

The first set of pulses (PY) is sent to the six-pulse bridge
connected to the wye (Y) secondary winding of the Y/Y/Delta converter
transformer. The second set of pulses (PD) is sent to the six-pulse
bridge connected to the delta secondary winding of the converter transformer.
The PD pulses can be set to lead or lag the PY pulses by 30 electrical
degrees, depending on the configuration of the delta connection of
the converter transformer.

The following figure shows an example of a Pulse Generator (Thyristor)
block connected to a twelve-pulse thyristor converter.

The Pulse Generator (Thyristor) block can be programmed to control
a six-pulse thyristor converter made of one three-phase full-wave
thyristor bridge. In this configuration, the PD pulse train is not
generated and the block outputs only the PY pulse train. The pulse
train, renamed P, is suitable for a Graetz bridge connected to a converter
transformer, with no phase shift between primary and secondary windings.

The pulse ordering in the pulse trains corresponds to the natural
order of commutation of a three-phase thyristor bridge, as shown in
the following figure.

The table below gives the commutating voltages for the thyristors
according to the transformer conection. The transformer conection
reflects the phase shift between the AC source and the thyristors.

Thyristor to be ignited

1

2

3

4

5

6

Thyristor to be extinguished

5

6

1

2

3

4

Commutating voltage for a Y-Y conection

Vac

Vbc

Vba

Vca

Vcb

Vab

for a Y-D1 (lagging)

-Vc

Vb

-Va

Vc

-Vb

Va

for a Y-D11 (leading)

Va

-Vc

Vb

-Va

Vc

-Vb

The Pulse Generator (Thyristor) block is controlled by the alpha
angle reference signal and by the synchronization signal wt.
The wt signal is an angle varying between 0 and 2*pi radians, synchronized
on zero crossings of the fundamental (positive-sequence) of phase
A of the primary voltage of the converter transformer. The wt signal
is normally obtained from a phase locked loop (PLL) system.

The Pulse Generator (Thyristor) block generates internal wt
ramps to control the pulses. The alpha delay angle is expressed in
electrical degrees by which the pulse is delayed relative to angle
zero of its commutating voltage. The figure shows how the PY pulse
train is generated.

The Pulse Generator (Thyristor) block can be configured to work
in double-pulsing mode. In this mode two pulses are sent to each thyristor:
a first pulse when the alpha angle is reached, and then a second pulse
60 degrees later, when the next thyristor is fired. This figure shows
the double pulses in a PY pulse train.

Dialog Box and Parameters

Generator type

Select the type of thyristor converter to control. When set
to 6-pulse, the PD pulse train output is
not generated, and the PY output is renamed to P.

Delta winding connection

Specify the type of delta secondary winding connection of the
converter transformer. When set to D1(lagging),
the PD pulses lag the PY pulses by 30 degrees. When set to D11(leading),
the PD pulses lead the PY pulses by 30 degrees.

Pulse width (deg)

Specify the width of the pulses, in degrees.

Double pulsing

When this check box is selected, the Pulse Generator (Thyristor)
block implements the double-pulsing technique.

Sample time

Specify the sample time of the block, in seconds. Set to 0 to
implement a continuous block.

Inputs and Outputs

alpha

The alpha delay angle signal, in degrees. This input can be
connected to a Constant block, or it can be connected to a controller
system to control the pulses of the generator.

wt

Angle, in radians, varying between 0 and 2*pi, synchronized
on zero crossings of the fundamental (positive-sequence) of phase
A of the primary voltage of the converter transformer. The wt signal
is normally obtained from a phase locked loop (PLL) system.

Block

When set to true (Boolean 1), blocks the operation of the generator.
The pulses are disabled and block the operation of the generator.

PY, P

Outputs the six-pulse signals to be sent to the six-pulse thyristor
converter connected to the Y secondary winding of the converter transformer.
The output is named PY when the Generator
type parameter is set to 12-pulse, and named PY when the Generator
type parameter is set to 6-pulse.

PD

Outputs the six-pulse signals to be sent to the six-pulse thyristor
converter connected to the Delta (D) secondary winding of the converter
transformer. This output does not exist when the Generator
type parameter is set to 6-pulse.